Download methods

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Object methods
Database system
Database
management
system
Database
SQL object
methods
External
SQL object
methods
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Use of object methods
Table with object collection
Virtual relational table
Table()
Object view
Method4
Method5
Method6
select …
from …
where …
Method1
Method2
Method3
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Types of object methods
Object methods (also known as subprograms) are functions or procedures
that you can declare in an object type definition to implement behavior that
you want objects of that type to perform. The general kinds of methods that
can be declared in a type definition are:
1. Member methods. Using member methods, you can provide access to the
data of an object, and otherwise define operations that an application
performs on the data. To perform an operation, the application calls the
appropriate method on the appropriate object.
1) comparison methods:
a) MAP MEMBER function;
b) ORDER MEMBER function.
2) non-comparison member methods:
a) MEMBER function;
b) MEMBER procedure.
Member methods have a built-in parameter named SELF that denotes the
object instance currently invoking the method. SELF can be explicitly
declared, but that is not necessary. It is simpler to write member methods that
reference the attributes and methods of SELF implicitly without the SELF
qualifier.
2. Static methods. Static methods compare object instances and perform
operations that do not use the data of any particular object, but, instead, are
global to an object type.
3. Constructor methods. A default constructor method is implicitly defined
for every object type, unless it is overwritten with a user-defined constructor.
A constructor method is called on a type to construct or create an object
instance of the type.
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Object methods
1. Constructor method.
2. MAP Member method.
3. ORDER Member method.
4. MEMBER method.
5. STATIC method.
a)
MAP MEMBER
method
SELECT ...
FROM ...
WHERE ...
ORDER BY ...
SELF pbjekti
b)
ORDER MEMBER
method
c)
OSQL
MEMBER method
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Subprograms in database
Subprograms can be written in:
1) PL/SQL language;
2) virtually in any other programming language.
Methods written in PL/SQL or Java are stored in the database.
Methods written in other languages, such as C, are stored externally.
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Guidelines for comparison methods
You can declare:
1) a Map Member method;
2) an Order Member method (but not both).
For either method type, you can compare objects using SQL statements and
PL/SQL procedural statements. However, if you do not declare one of these
methods, you can only compare objects in SQL statements, and only for
equality or inequality.
Two objects of the same type are considered equal only if the values of their
corresponding attributes are equal.
When sorting or merging a large number of objects, use a map method,
which maps all the objects into scalars, then sorts the scalars. An order
method is less efficient because it must be called repeatedly (it can compare
only two objects at a time).
a)
MAP MEMBER
method
SELECT ...
FROM ...
WHERE ...
ORDER BY ...
SELF objects
b)
ORDER MEMBER
method
SELF objects
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Comparison methods in type hierarchies
In a type hierarchy, if the root type (supertype) does not specify a map or an
order method, neither can the subtypes.
If the root type specifies a map method, any of its subtypes can override it.
If the root type does not specify a map method, no subtype can specify one
either.
Only the root type can define an order method. If the root type does not
define one, its subtypes cannot add one.
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Definition of object types
1) specification
create or replace type ...
2) body
create or replace type body ...
create or replace type SCHEMA.TYPE as object(
parameterdata_type,
parameterdata_TYPE,
…,
MAP Member FUNCTION ...,
ORDER Member FUNCTION ...,
MEMBER ...,
STATIC ...);